This application discloses an improvement of a blood pressure measuring device disclosed in copending application Ser. No. 892,848, filed Aug. 1, 1986, now U.S. Pat. No. 4,796,184 and assigned to the assignee of this application; and copending application Ser. No. 024,662, filed Mar. 11, 1987, pending and assigned to the assignee of this application. More particularly, this invention relates to an improved blood pressure measuring device which can provide more accurate determinations of mean arterial blood pressure.
The measurement of systolic, diastolic and mean arterial blood pressure values by measuring cuff pressure oscillations caused by blood vessel pulses during stepwise deflation of the cuff is a known technique. Methodology and apparatus for automatically performing this general procedure are disclosed in U.S. Pat. No. 4,349,034 granted Sept. 14, 1982 to M. Ramsey and U.S. Pat. No. 4,360,029 granted Nov. 23, 1982 to M. Ramsey. These patent disclosures relate to a technique which uses a computer controlled device to inflate a pressure cuff, stepwise deflate the cuff, measure and store cuff pressure oscillations occuring at each deflation plateau, and determine which cuff pressure oscillation was the largest. The device then identifies the cuff pressure at which the largest oscillation took place as the mean blood pressure. Provisions are made for rejecting artifact cuff pressure oscillations which can result from subject movement, accidental contact with the pressure cuff, and the like.
A device similar to that disclosed in the aforesaid patents is described in an article authored by Joseph Erlanger, M.D., published in The Johns Hopkins Hospital Reports Vo. XII by the Johns Hopkins Press (1904). In the Erlanger device, the cuff was automatically inflated to an initial pressure above mean, and then stepwise deflated to a pressure below mean. Cuff pressure oscillations were sensed and traced onto a rotating drum sheet by a floating pen. Artifact oscillations are apparent upon viewing the trace.
The devices described in the aforesaid patents and in the Johns Hopkins Reports all rely on the largest cuff pressure oscillation as identifying true mean blood pressure. It will be readily appreciated that such reliance is misplaced since the likelihood of the largest observed cuff pressure oscillation actually occuring exactly at the true mean blood pressure is remote. The device disclosed in copending application Ser. No. 892,848 identified above uses the greatest cuff pressure oscillation observed, along with the next greatest observed oscillation of each side thereof to calculate a parabolic curve. The zenith of the calculated curve is then used to identify true mean blood pressure. One problem that sometimes arises with the latter approach is that the calculated parabolic curves can be skewed to the wrong side of the highest observed oscillation. This is due to our observations that cuff pressure oscillations descend at a more rapid rate than they rise when the oscillations are taken at preset cuff pressure increments.